Massachusetts General Laws
Chapter 142 - Supervision of Plumbing
Section 19 - Safety Devices for Hot Water Tanks; Statements by Manufacturer; Approval; Pipes and Fittings

Section 19. No hot water tank shall be installed and connected unless it is protected with safety devices as follows:—
A. A hot water tank in which water is to be heated or stored under pressure greater than fifteen pounds per square inch shall be equipped with a suitable pressure relief valve installed in a tapping in the tank or in the cold water supply line, or the hot water outlet line, with no shut-off valve between the relief valve and the tank. The pressure relief valve shall be set by the manufacturer to operate at a pressure not more than the maximum working pressure stamped on the tank or jacket or casing, and shall be so constructed that said setting cannot be exceeded by normal means of adjustment.
B. A hot water tank to which a heating device or appliance capable of delivering water to the tank at a temperature greater than two hundred and twelve degrees Fahrenheit is connected shall be equipped with a suitable temperature relief valve so adjusted and installed as to prevent development of, or accumulation of, water which is at a temperature in excess of two hundred and twelve degrees Fahrenheit. Said temperature relief valve shall be installed in a tapping directly in or on the tank, within twelve inches of the top of a vertical tank, or within six inches of the top of a horizontal tank, with no fittings between the valve and the tank, except that a bushing may be used to reduce the tapping to fit the valve, or the valve shall be installed in the hot water outlet pipe as close to the top of the tank as possible. In no case shall the heat sensitive member of the temperature relief valve be more than five inches away from the top of the tank. The discharge outlet of the temperature relief valve shall be connected by means of a non-ferrous pipe or tubing not less than three eighths inch inside diameter, with no shut-off, to an open plumbing fixture, or to within twelve inches of the basement floor. A thermostatically controlled hot water tank may be protected by an automatic fuel shut-off device in addition to the thermostat. Such shut-off device shall be installed in the same location and perform the same function as said temperature relief valve.
C. All parts of temperature and pressure relief valves which are in contact with water shall be made of non-ferrous metals or materials having suitable corrosion resisting properties. All pipe and fittings between relief valves and the hot water tank shall be of non-ferrous metals.
D. Relief valves shall be marked by the manufacturer, by stamping or casting in the metal of the valve, or on a metal tag permanently attached to the valve, as follows:—
1. Manufacturer's name or registered trade mark.
2. The type or style, or the type and style, of the valve.
3. The pressure setting of the valve in pounds per square inch.
4. The temperature setting in degrees Fahrenheit.
5. Temperature relieving capacity in B.T.U. per hour.
Notwithstanding the requirements of paragraph B of this section, the protective devices specified therein shall not be required in the case of that portion of tankless water heaters which contain water to be heated or stored under the provisions of section seventeen. Said portion of tankless water heaters shall be equipped with a pressure relief valve and an automatic tempering device, set to deliver water not exceeding one hundred and eighty degrees Fahrenheit and located between said tankless water heater and any hot water supply pipe which it serves.
All pipes and fittings between the tankless water heater and the pressure relief valve and the tempering device shall be of non-ferrous metals. All parts of the tempering device which are in contact with the water shall be of non-ferrous metals or other materials having suitable corrosion-resisting properties. Said tempering device shall be marked by the manufacturer by casting or stamping in the metal of the device, or on a metal tag permanently attached to the device, as follows:—
1. Manufacturer's name or registered trade name.
2. The type or style, or the type and style, of the device.
3. The temperature settings, in degrees Fahrenheit, plainly marked.
E. Temperature and pressure relief valves and other devices referred to in this section shall be subject to the approval of the inspectors of plumbing or other proper authorities.
F. All pipes and fittings in the circulating system between a hot water tank and the heating device or appliance shall be non-ferrous, and of ample size so as to make it possible to heat seventy-five per cent of the available water in the tank without raising the temperature of any part of the water above two hundred and twelve degrees Fahrenheit.
G. No hot water tank shall be installed without being equipped with an approved device located so as to prevent any partial vacuum therein.